It usually comes from oily fish such as herring, tuna, anchovies and mackerel. Yet sometimes it's produced from the livers of other fish, as is the case with cod liver oil.

The World Health Organization (WHO) recommends eating 1–2 portions of fish per week. This is because the omega-3 fatty acids in fish provide many health benefits, including helping protect against a number of diseases.

But if you don't eat 1–2 portions of fish per week, fish oil supplements can help you get enough omega-3s.

Around 30% of fish oil is made up of omega-3s, while the remaining 70% is made up of other fats. Also, unprocessed fish oil contains some vitamin A and D.

It's important to note that the types of omega-3s found in fish oil have greater health benefits than the omega-3s found in some plant sources.

The main omega-3s in fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), while the omega-3 in plant sources is mainly alpha-linolenic acid (ALA).

Although ALA is an important essential fatty acid, EPA and DHA have many more health benefits (, ).

Another reason it's important to get enough omega-3s is because the Western diet has replaced a lot of omega-3s with other fats like omega-6s. This distorted ratio of fatty acids may contribute to a number of Western lifestyle diseases (, , , ).

Your brain is made up of nearly 60% fat, and much of this fat is omega-3 fatty acids. Therefore, omega-3s are essential for normal brain function (, ).

In fact, some studies have shown that people with certain mental disorders have lower omega-3 blood levels (, , ).

Interestingly, studies have shown that fish oil supplementation can prevent the onset or improve the symptoms of some mental disorders. For example, it can reduce the risk of psychotic disorders in those who are at risk (, ).

In addition, supplementing with fish oil in high doses can reduce some symptoms of both schizophrenia and bipolar disorder (, , , , , ).

Bottom Line: Fish oil supplementation can improve the symptoms of certain psychiatric disorders. This effect may be a result of increasing omega-3 fatty acid intake.

Obesity is defined as having a body mass index (BMI) greater than 30. Globally, about 39% of adults are overweight, while 13% are obese. The numbers are even higher in high-income countries like the US ().

Obesity can significantly increase the risk of other diseases, including heart disease, type 2 diabetes and cancer (, , ).

Similarly to the brain, omega-3 fats make up an important part of the structure of the eye. Evidence has shown that people who don't get enough omega-3s have a greater risk of eye diseases (, ).

Furthermore, eye health begins to decline in old age, which can lead to age-related macular degeneration (AMD). Eating fish seems to help prevent AMD, but the results on fish oil supplementation are less convincing (, ).

One study found that consuming a high dose of fish oil for four and a half months improved vision in all AMD patients. However, this was a very small study ().

Two larger studies examined the combined effect of omega-3s and other nutrients on AMD. One study showed a positive effect, while the other showed no effect. Therefore, the results are unclear (, ).

Bottom Line: Eating fish may help prevent eye diseases. However, it's unclear whether fish oil supplementation has this same effect.

Maternal and early fish oil supplementation may also improve infant visual development and help reduce the risk of allergies (, ).

Bottom Line: Omega-3 fatty acids are essential for early growth and development. Fish oil supplementation in mothers or infants may improve eye development, although its effect on learning and IQ is unclear.

Dosage

EPA and DHA dosage recommendations vary depending on your age and health.

The World Health Organization (WHO) recommends a daily intake of 0.2–0.5 grams of combined EPA and DHA. But it may be necessary to increase the dosage if you are pregnant, nursing or at risk of heart disease ().

Choose a fish oil supplement that provides at least 0.3 grams (300 mg) of EPA and DHA per serving.

Form

Ethyl esters are not absorbed by the body as well as the others, so try to choose a fish oil supplement that comes in one of the other listed forms ().

Concentration

Many supplements contain up to 1,000 mg of fish oil per serving but only 300 mg of EPA and DHA.

Read the label and choose a supplement that contains at least 500 mg of EPA and DHA per 1,000 mg of fish oil.

Purity

A number of fish oil supplements don't contain what they say they do ().

To avoid these products, choose a supplement that is "third-party tested" or has the standard of purity.

Freshness

Omega-3 fatty acids are prone to oxidation, which makes them go rancid.

To avoid this, you can choose a supplement that contains an antioxidant, such as vitamin E. Also, keep your supplements away from light, ideally in the refrigerator.

Don't use a fish oil supplement that has a rancid smell or is out of date.

Sustainability

Choose a fish oil supplement that has a sustainability certification, such as from the (MSC) or the .

The production of fish oil from anchovies and similar small fish is more sustainable than the production of fish oil from large fish.

Timing

Other dietary fats help the absorption of omega-3 fatty acids ().

Therefore, it's best to take your fish oil supplement with a meal that contains fat.

Bottom Line: Check the instruction label of a fish oil supplement before consumption. Also, choose a supplement with a high concentration of EPA and DHA and that has purity and sustainability certifications.